Lectures 12 & 13 Anatomy and Physiology of Skeletal Muscles.pdf

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Lectures 12 & 13: Anatomy andPhysiology of Skeletal MuscleMartini et al. Mods 9.1-9.14, pp. 307-333Universal characteristics of muscle tissueMicroscopic anatomy of skeletal muscle: themuscle fiber, myofilaments, striationsStructure and function at the neuromuscularjunctionThe sliding filament theory of muscle contractionBehavior of whole muscles
Universal Characteristics of MuscleResponsiveness (excitability):Chemical signals, stretch,other stimuli produce electrical changes across the plasmamembraneConductivity:Local electrical change triggers a wave ofexcitation that travels along the muscle fiberContractility:Shortens when stimulated to exert force ontissues and organs and to create movementExtensibility:Capable of being stretched betweencontractionsElasticity:Returns to its original resting length after beingstretched
___?___Muscle(a)Muscle cellsNuclei(b)___?___muscle: Lacks striationsand isinvoluntary___?___muscle—forms layers of digestive, respiratory, andurinary tract: propels contents through an organ, regulatesdiameter of blood vessels
___?___Muscle___?___muscle:Limited to theheartStriated and involuntary(a)(b)GlycogenStriationsIntercalated discs
___?___Muscle___?___muscle: made of long, thread-like cells withmultiple nuclei calledmuscle fibersMost attach to bone via tendonsStriations—alternating dark and light bands from overlap ofcontractile proteinsVoluntary(a)StriationsMuscle fiber(b)Nuclei
Sarcoplasm:cytoplasm of a muscle fiberSarcolemma:plasma membrane of a muscle fiberSarcoplasmic reticulum:smooth ERthat forms a network around eachmyofibril and stores the calciumthat activates the musclecontraction processMitochondriaMyofibrils:longprotein bundles thatoccupy the mainportion of thesarcoplasmMyofilamentsA bandI bandZ discNucleusMusclefiberThe Muscle Fiber = The Muscle CELLProtein Molecules < Myofilament < Myofibril < Muscle Fiber
(a)Myosin moleculeHead(b)Thick filamentMyosin headMyofilamentsThick filaments: made of several hundredmyosinmoleculesThin filaments:actin,tropomyosin, andtroponinmoleculesElastic filaments:titin (huge, springy protein thatprevents overstretching)Tail
MyofilamentsContractile proteins—myosinandactindo the workRegulatory proteins—tropomyosinandtroponinLike a switch that determines when the fiber can contract andwhen it cannotContraction activated by release ofcalciuminto sarcoplasm andits binding totroponin(b)Thick filamentMyosin head(c)Thin filamentTroponin complexG actinTropomyosin
StriationsMyosinandactinare proteins that occur in all cellsOrganized in a precise way in skeletal and cardiac muscleA (anisotropic) band:dArk, particularly where thick and thinfilaments overlapI (isotropic) band:alternating lIghter bandZ disc:provides anchorage for thin filaments and elastic filamentsSarcomereI bandI bandA bandThick filamentThin filamentElastic filamentZ discZ disc

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muscle tension, Physiology of Skeletal Muscle

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